Measurement of high np Rydberg states and the ionization potential of H2

Abstract

Using double-resonance spectroscopy through the E1F1Σ g + state of molecular hydrogen, we measured transitions to several singlet npRydberg states. The E,Fstate is excited by a two-photon transition at 202 nm using laser radiation generated by sum frequency mixing in β-BaB2O4. A pulse-amplified frequency-doubled cw dye laser is used to excite Rydberg states with nup to 100 from the E,Fstate. The transition wavelengths have been determined to an accuracy of 0.004 cm−1. By combining these measurements with our earlier determination of the E,Fstate energy levels to an accuracy of 0.01 cm−1, the absolute term energies can be determined. Simple quantum defect treatments describe the P(1), Q(1), and R(0) branches accurately and yield a value for the ionization potential accurate to ~0.015 cm−1, an improvement by nearly an order of magnitude over the best previous work. Our preliminary result of 124417.526 cm−1 is in good agreement with theoretical calculations that include relativistic and radiative corrections. A final result for the IP is presented. The structure and decay mechanisms of the high Rydberg npstates are also discussed.